ASSESSMENT OF “PILED-RAFT” FOUNDATION DESIGN PRACTICE IN ADDIS ABABA


Author/s

MAHIDERE MAMO AND HENOK F. GEBREGZIABHER


Abstract

Piled rafts are deep foundation types which account for the bearing capacity of the raft that is otherwise ignored traditionally. Since the raft rests on the ground, the traditional design method is excessively conservative as the raft is considered as an additional load on the piles rather than being a supporting structure. As an extension of the world-wide applications, piled rafts are getting attention in Ethiopia, most particularly in Addis Ababa. The present research dealt with the assessment of some of the deep foundations for high-rise buildings in Addis Ababa. Based on three dimensional analyses of three representative high-rise buildings in the city, it has been found out that the foundations are practically performing as conventional pile foundations even if designed as “piled rafts”. While the customary use of closely spaced piles leads to such conservative results, further parametric studies with reduced number of piles indicates that the use of wider pile spacing is recommended to be used for activating the raft in the load share of the foundation.